Among current remedial options, the permeable reactive barrier (PRB) market segment is evolving and gaining popularity as a promising technology in terms of cost and stability of performance. However, several problems are prevalent with conventional PRB systems. Typically, there is no ability to exchange permeable reactive materials (PRMs) emplaced in subsurface trenches should laboratory treatability tests and remedial planning efforts fail to accurately predict the geochemical reactions that occur in the subsurface environment, resulting in a reduction in the system's longevity. Also, disposing of large excavated volumes of contaminated material from trenches required for the installation of conventional PRB systems is not well addressed.
Another problem is the restricted placement of conventional PRB systems at distal portions of plumes due to limitations on the ability to effectively treat contaminant mass flux. Finally, there is typically an inability to rehabilitate areas where mineral precipitation may occur within the PRMs or adjacent formations. These problems affect remediation contractors because conventional PRB remedial systems may not last as long as predicted and may require injections, or in the worst case, expensive re-excavation, which can involve remobilization of construction equipment and handling and disposal of hazardous waste generated from the re-excavation and the PRB re-emplacement processes.
A technically viable and cost-effective solution is therefore needed due to current PRB design, performance, and longevity concerns. Improvements are needed in PRB construction methods and installations to increase performance and allow flexibility in treating multiple and mixed groundwater contaminants.
Current methods for driving conventional large-diameter pipe piles (i.e., 10-inches in diameter or greater) into the ground rely on vibratory hammers. In most conventional construction applications, the pipe piles are open on the bottom making it easier to drive the pile to the target depth. In typical construction applications pipe piles do not have well screens embedded in their walls that require protection during installation.
This disclosure describes the devices for driving large-diameter pipe piles with well screens (filter casings) into the subsurface for use in remediating contaminated groundwater. Methods are described for installing an artificial gravel pack in the resulting annular space created between the internal wall of the drive device and the external wall of the filter casing for promoting contaminant flow to the inlet screen area and minimizing the quantity of fine particles that could otherwise impede the flow of contaminants into the inlet screen area or treated water from flowing out the outlet screen area. In addition, the methods described for installation provide protection for the screen areas while the filter casing and its related components are driven into a potentially resistive subsurface environment.
NAPLs typically occur in separate, immiscible phases with varying degrees of solubility. In the subsurface environment NAPLs are generally distinguished by two types based on their density relative to groundwater. Light non-aqueous phase liquids (LNAPLs) are groundwater contaminants such as petroleum-based products that are less dense than water. The LNAPL constituents can occur in four physical states and may partition or move from one phase to another depending on the conditions in the subsurface environment.
Once LNAPLs have migrated from a source area downward under the force of gravity through the unsaturated zone and approach the water table, the LNAPLs may temporarily depress the water table and move laterally in several directions along the upper boundary of the zone of saturation. However, once the source has been removed, and given time, the water table will rebound and the LNAPLs will migrate generally in a downgradient direction on the top of the water table. Soluble components of the LNAPLs will dissolve and form an aqueous-phase groundwater contaminant plume. Other phases of the LNAPL constituents in the subsurface may include a gaseous phase (where volatilization may spread the contaminant upward toward the land surface) or in a solid phase (where the constituents adsorb on a solid surface, such as soil particles or the aquifer matrix).
Dense non-aqueous phase liquids (DNAPLs) are groundwater contaminants that are denser than water (specific gravity [SG] greater than 1.0). Some NAPLs such as No. 6 fuel oil may exist as an LNAPL with an SG less than 1.0, or as a DNAPL with an SG of 1.05. Other common DNAPLs include a variety of chlorinated solvents used for degreasing such as trichloroethylene (TCE) and tetrachloroethene (PCE), coal tar associated with manufactured gas plants, carbon tetrachloride (CCl4) used as a grain fumigant, transformer and insulating oils containing polychlorinated biphenyls (PCBs), and timber-treating oils such as creosote. Unlike LNAPLs, the DNAPLs can migrate to considerable depths below the ground surface and reside upon low permeability clay lenses within the aquifer or on the base of aquifer where the DNAPLs can then slowly dissolve and form aqueous phase plumes in groundwater.
NAPLs create unique challenges for site characterization and groundwater remediation. Should a conceptual site model (CSM) indicate that NAPLs are known or suspected in an aquifer, then investigative approaches based on the CSM can be used to avoid vertical cross contamination while promoting the effective capture of NAPLs. It is important to consider the NAPL properties, physical states, distribution, degradation, interactions with aquifer media, and expected behavior in the subsurface environment as part of the CSM.
The present disclosure relates to the capture of NAPLs in the groundwater using removable skimmer cartridges containing super absorbent polymers or equivalent and emplaced in filter casings. The specifications of the filter casing can be based on the CSM. The filter casings can serve two other remedial purposes, as appropriate: 1) collection of the gaseous phase of NAPLs, and 2) housing separate removable cartridges for the treatment of the dissolved phases of NAPLs.
Current methods for remediating contaminated sediments in surface water bodies generally include in-situ approaches (e.g., capping, institutional controls, monitored natural recovery, and treatment) and ex-situ approaches (e.g., dredging [conducted under water] and excavation [typically conducted after water has been diverted or drained from the water body]). This disclosure describes a technology for treating contaminated water in sediment once it has been dredged, excavated, or otherwise removed from water bodies and placed in an above ground containment system for drainage and evaporation.
The above ground containment system stores sediment that has been removed from water bodies for the dewatering and treatment process, and in some situations, potentially serves as a long-term sediment storage option.
Many shallow aquifers are directly connected to, and in continuing interaction with, surface water, which is why groundwater and surface water are viewed as a single resource by the U.S. Geological Survey. Contaminated surface water can negatively impact the groundwater quality in an aquifer for long periods of time. Similarly, contaminated aquifers that discharge into surface water can impair the quality of the surface water. Human activities that have impacted water resources are usually described by either discrete and localized point sources, or by diffuse nonpoint sources that occur over broader geographic areas.
Examples of point sources include, but are not limited to: 1) leaking storage tanks or pipelines, accidental spills at manufacturing facilities or on roadways, landfills, graveyards, septic fields; 2) runoff from waste disposal sites, mines, oil fields, industrial sites, military bases, construction sites, and animal feedlots; 3) industrial wastewater effluents, for example, steel plants, pulp and paper mills, food-processing plants; and 4) overflow from combined storm and sanitary sewer systems. Examples of nonpoint sources that can impact water resources over a broad geographic area include agricultural runoff, stormwater and urban runoff, runoff from large construction sites, and atmospheric deposition of contaminants.
The present disclosure offers apparatus and methods for containing and treating contaminated groundwater, surface water, or combined groundwater and surface water primarily originating from discrete point sources of limited geographic extent using a trench-based remedial system. The invention could also be used for spill prevention, control, and countermeasure (SPCC) efforts near facilities that store or transmit hazardous materials; for example, downhill of above ground storage tanks that are located near sensitive environmental areas.